The present invention refers to an apparatus, particularly an electro-erosion apparatus for machining workpieces, having a machine table for receiving a workpiece, a first machining head, at least two degrees of freedom of movement of the apparatus in and/or parallel to the main working plane of the workpiece (X/Y-plane) and at least one additional degree of freedom of the movement perpendicular to the main working plane (Z-axis). The invention also refers to a method of machining workpieces, particularly an electro-erosive method, in which a workpiece on a machine table is machined with a first machining head in at least two directions of movement in and/or parallel to the main working plane of the workpiece (X/Y-plane) and at least one additional direction (Z-axis) perpendicular to the main machining plane.
Such apparatus and methods of machining are known, for instance, from milling machines or electro-erosion sinker machines.
In the following a terminology is used which serves for the easier reading of the specification but is not to be understood in a limitative manner. For example, the expressions top/bottom, larger/smaller, etc., refer to machines of ordinary operational setup and size.
In apparatus of the aforementioned type, the path of displacement of the machine in the X/Y-plane of the workpiece is determined by the paths of travel of a machine table and/or of an upper carriage.
In electro-erosion sinker machines, particularly medium sized and large machines, there is a functional relationship between desired electrode weights and weights used in practice and the displacement paths of the machine.
In general, in the case of electrodes of high weights, very small travel paths are required (in the case of planetary movements and upon scanning of references upon the adjustment of workpieces) while with small electrode weights a path of travel over the entire size of the table is desired (in the case of local machining with small electrodes).
This results from the different possibilities of use of such electrodes. Small electrodes, for instance electrodes in pin-shape or other simple geometric shapes, can be used among other things for the manufacture of complex shapes and for erosion machining in several directions of movement. In this connection, for instance, a plurality of different small electrodes are preferably employed with which individual sections of the workpiece are machined. The weight of such electrodes tends to be slight. The use of this operating technique is possible by modem CNC control techniques which make it possible in very simple fashion to effect a precise positioning of the electrodes. Another advantage of the use of small electrodes resides in their simpler manufacture and, of course, in the uncomplicated replacement of individual electrodes which are particularly worn.
The smaller paths of travel of large electrodes are explained in similar manner. Frequently, a large electrode having a complicated pattern is simply lowered, without further machining in the X/Y-plane, in Z-direction into the workpiece. Here, on basis of slight displacements of the electrode still before the start of the sinker, a coordinate zero point must be determined by the scanning of reference points.
Summarizing, it can thus be stated that there is a particular need for machines with a large path of travel for small electrode weights.
Machines with a moveable portal have relatively large paths of travel in one direction of the plane of the workpiece (X longitudinal direction) but not in the other (Y transverse direction). Larger paths of displacement are obtained with a portal construction having two discharge heads which are independent of each other. In this case, a second head of reduced supporting force is fastened by an additional shaft on the transverse beam of the bridge. This solution, however, is relatively expensive. In machines of C-type construction, customary variants are for instance, machines having a displaceable compound table and ones with upper displaceable carriages - the essential advantage as compared with the portal construction resides in the lower cost. An increase in the displacement paths has up to now always meant a substantial increase in the machine expenses since the dimensioning is determined by the maximum electrode weight or workpiece weight.